The prime minister said that he was "devastated" by the news that Shale, aged 56, had been found dead in a portable toilet at the festival, after apparently suffering from a heart attack. Early rumours that he may have committed suicide were rejected by police.

It has emerged that two Downing Street officials tried to reach Shale around lunchtime on Saturday to warn him about the note, in which he described parts of his local party as crass and grasping and said that it offered people no reason to join, had been passed to the Mail on Sunday.

One official contacted him by text just after 12.30pm to advise him not to speak to reporters; another suggested he get in touch with Conservative headquarters.

Shale subsequently contacted the Witney constituency agent Barry Norton, a West Oxfordshire councillor, who said that Shale had been aware of the Mail article but was "quite confident that this was not really an issue".

According to a family friend who has been briefed by medical staff, doctors believe Shale may have suffered a massive heart attack as early as lunchtime on Saturday. There are reports that his family has a history of heart disease, and there is no evidence linking his having heard about the leak to the heart attack.

The prime minister said the death had left him and his wife, Samantha, devastated, and that "a big rock in my life has suddenly been rolled away".

Cameron had been aware of the note's existence and there is deep concern inside Downing Street that its contents, known only to a small number of people, had been disclosed.

The paper was essentially a strategy document setting out how to recruit members. It said the local party appeared "graceless, voracious, crass, always on the take", and needed to radically change.

Judging by its blunt language, the memo was clearly not written for wide circulation in his local party.

Early reports of the death, including one from the Glastonbury festival organiser, Michael Eavis, suggesting that Shale had killed himself, were dismissed as inaccurate. Avon and Somerset police said that the death was not being treated as suspicious.

Party officials had said earlier that there was no suggestion from Shale's behaviour that he was overly concerned about the leak.

Shale's contacts with Downing Street officials were seen as routine and polite, and he is not believed to have taken up the advice to speak to the party headquarters. One senior party source said the heart attack was "just a dreadful coincidence", adding: "The story in the Mail on Sunday did not concern us that much."

After the texts, Shale did contact Norton, who said: "He was absolutely in good health. We understand that his death has been as the result of a heart attack, that is the information we have. There's a history of that in his family and anything to the contrary, at the moment, is totally scurrilous."

Asked if Shale had been aware of the Mail article, he said: "Yes he was. He was very aware of that article. He was very circumspect with it, and was quite confident that this was something that was not really an issue. And he was looking forward to increasing our membership, and was working on a pilot to do that."

It was pointed out that Shale, 56, who worked in PR, management consultancy and marketing, was a robust character not to be fazed by the interplay of media and politics. He had been staying in one of the luxury caravans behind the Pyramid Stage. His wife raised the alarm early in the morning, but his body was not found until 9am. Rupert Soames, a businessman and friend of Shale who was at Glastonbury and had helped co-ordinate arrangements following his death, said through a spokesman that medics had told him and Shale's family that they believed he had died of a massive heart attack at "around lunchtime" on Saturday.

The prime minister, MP for Witney in Oxfordshire for 10 years, said Shale had been "a huge support" over the decade. Cameron said: "Christopher was one of the most truly generous people I've ever met – he was always giving to others, his time, his help, his enthusiasm, and above all his love of life. It was in that spirit that he made a massive contribution to the Conservative party. Our love and prayers are with Nikki and the family. They've lost an amazing dad, west Oxfordshire has lost a big and wonderful man, and, like so many others, Sam and I have lost a close and valued friend."

In a statement, Eavis said: "I would like to express my deepest sympathy to [Shale's] family and friends."

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